Method of making edgewise wound resistance coils



J. F. FRESE 2,061,516

METHOD OF MAKING EDGEWISE WOUND RESISTANCE COILS Nov. 17, 193.6.

Filed Nov. 20, 1935 2 Sheets-Sheet 1 Nov. 17,1936, v J; F. FRESE 2,061,516

METHOD OF MAKING EDGEWISE WOUND RESISTANCE COILS Filed Nov. 20, 1955 I 2 Sheets-Sheet 2 Patented Nov. 17, 1936 PATENT OFFICE METHOD OF MAKING EDGEWISE WOUND RESISTANCE COILS Joseph F. Frese, Baltimore, Md., assignor to Monitor Controller Company, Baltimore, Md., a corporation of Maryland Application November 20, 1935, Serial No. 50,796

1 Claim.

This invention relates to improvements in a method of making edgewise wound resistance coils. In the patent to George H. Whittingham Number 1,687,357, dated October 9, 1928 are shown resistance units arranged in banks, each unit consisting of a fiat metal bar having an insulating covering with teeth on its opposite edges and a coil composed of a ribbon of resistance metal wound on edge, the coil being threaded onto the covering and its convolutions being spaced apart by the teeth. The main purpose of the present invention is to provide an edgewise wound coil which, for a given length of coil, will have a greater length of ribbon than a plain edgewise wound coil made from a ribbon of the same width and thickness. Thus, a coil made in accordance with the present invention from a strip of resistance metal of given width and thickness, while occupying the same lineal space on a supporting core of the kind disclosed in said patent, will have several times the total resistance of the plain coil.

In the accompanying drawings,

Fig. 1 is a side elevation of a resistance unit having an edgewise wound coil made in accordance with my invention, the end portions only of the coil being shown in full lines; a

Fig. 2 is a side elevation of a helix made from a fiat metal strip, illustrating the first step in the method of making the coil;

Fig. 3 is a cross-section through the same on volutions of the coil of Fig. 8 by pressure applied,

at the ends of the coil.

Referring to Figs. 1 to 6, inclusive, of the drawings, 0. represents a flat supporting bar having an insulating covering b provided with staggered teeth or projections I on its opposite edges and C indicates the edgewise wound coil of my invention threaded onto the insulator, the convolutions c of the coil being spaced apart by the teeth.

In making the coil in accordance with the method disclosed in Figs. 2 to 6, inclusive, a flat strip of resistance metal 2 is coiled closely into the form of a helically wound tube Figs. 2 and 3. This tube is then flattened by any suitable means,

forming a fiat zigzag strip 0 Figs. 4 and 5, in which the parts 3 at one side of the strip slope in one direction and are folded against the parts 3* at the opposite side of the strip which slope in the opposite direction. The zigzag folded strip 0 is then coiled on edge around a cylindrical bar in a suitable coiling machine which has the effect of stretching the strip toward the outer edge of the coil, as shown in Figs. 6 and 7, so that the folds 3 are pulled apart and the folds 3 are also pulled apart, leaving V-shaped gaps between the folds on each side of the coil, which gaps are crossed diagonally by the folds on the opposite side of the coil.

The zigzag edgewise wound coils may be made in continuous lengths and cut to suit the length of the insulating support. As compared with a plain edgewise wound coil made from a metal strip of the same Width and thickness, and having a sufficient number of convolutions to ill] the grooves on the supporting member, the zigzag coil, having the same number of convolutions, has several times the length of resistance strip and therefore several times the total resistance of the plain coil. While the folds of the zigzag coil cross one another and may be in close contact, the oxide on the metal is a sufiicient insulator to prevent shortcircuiting, the difference of potential between con,- tacting folds, when current is passing through the coil, being very small. Where straight resistors are desired instead of coiled ones, it will be evident that the flattened zigzag strip of Figs. 4 and 5 may be used.

Instead of flattening the helical tube and then coiling the flattened resistor on edge, a suitable length of the helical tube 0', shown in Figs. 2 and 3, may. be coiled closely around a core bar 4 to form a tubular coil 0 as shown in Fig. 8, and by then applying pressure to the ends of this coil, as illustrated in Fig. 9, its convolutions may be flattened into the form shown in Figs. 1, 6 and 7. In Patent to G. H. Whittingham 1,630,912, dated May 31, 1927, is shown a mechanism for coiling metal strips on edge and a similar mechanism may be adapted, with suitable modifications, to coiling the helical tube and flattening its convolutions. For the purpose of illustration, there is shown in Figs. 8 and 9 a core bar 4 having a face plate 5 secured thereto near one end. This core bar may be rotated by a motor 6 through gearing, not shown, and feed screws 1 may also be operated simultaneously by the motor to move a cross head 8 on guide rails 9 in the same way that a slide rest is moved in a lathe. By moving the cross head into a position close to the face plate and passing one end of ahelical tube c, like that shown in Figs. 2 and 3, through a guide tube II on the cross head and attaching said end to the face plate, and then starting the motor, the cross head will move away from the face plate and the tube will be coiled upon the core bar, as illustrated in Fig. 8. Then, while the motor is stopped, the cross head may be disconnected from the feed screws, as is done with the ordinary slide rest, and the cross head may be moved back toward the face plate to compress the tubular coil and flatten its convolutions, as shown at c in Fig. 9 and also as shown in Figs. 1, 6 and 7. The mechanism shown is only for the purpose of illustrating the method. I! desired, the core bar might be dc-clutched from the driving mechanism after the tubular coil has been wound upon it, and the feed screws could then be operated to move the cross head in either direction independently of the core bar to compress the coil and back the cross head oi! oi the bar to release the flattened coil, instead or releasing the cross head from the feed screws and moving it independently.

The method of making a fiat resistor which comprises winding a ribbon of resistance. metal helically into the form of a tube, coiling the tube into the form 01 a helix and then applying pressure to the ends 01 said helix to flatten its convolutions.

JOSEPH F. FRESE. 

